Ireland's deputy prime minister has warned the UK government his country "can't accept a time limit" on a Brexit backstop agreement aimed at preventing a hard border on the island of Ireland.

Simon Coveney, who is also Ireland's foreign minister, directly contradicted UK Brexit Secretary Dominic Raab's stance on a key part of the UK's withdrawal agreement.

As part of a divorce deal, the UK and EU are seeking a fallback agreement to avert a hard border between the Republic of Ireland and Northern Ireland, should a future EU-UK trade agreement not prevent this.

This could see either Northern Ireland or the whole UK effectively stay within the EU's customs union beyond Brexit day and the Brexit transition period.

"We can't accept a time limit, but we can accept it will only be there unless and until something better is agreed in the future, which is what everyone wants."

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Asked, if implemented, whether the proposed backstop would last months, years or decades, Mr Coveney replied: "With respect, that's up to the British government who need to decide what they want for the future."

Meanwhile, also on Friday and speaking in London following a difficult informal meeting of cabinet ministers in Downing Street, Mr Raab admitted the backstop issue is the "one real sticking point" in negotiations as he offered contradictory comments to Mr Coveney.

He said: "[The backstop] would have to be finite, it would have to be short and it would have to be, I think, time-limited in order for it to be supported here.

"What we cannot do is see the UK locked in via the backdoor to a customs union arrangement which would leave us in indefinite limbo, that would not be leaving the EU."

Mr Coveney also tempered expectations of a breakthrough on the Irish border backstop over the weekend.

"Whether that can happen as early next week I'm not sure, people need to be cautious on that," he said.

He denied the DUP's threats to vote down a Brexit deal and the UK government's budget if they do not consent to a backstop agreement meant there were impossible red lines preventing a deal.

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While highlighting the DUP's confidence and supply agreement with the Conservative government at Westminster, Mr Coveney warned of an "imbalance" being created in Northern Ireland politics.

He said: "The DUP represents a minority of people in Northern Ireland.

"The majority voted to stay in [the EU], though we have to respect the broad decision of the UK - and we do - but parties that represent the majority in Northern Ireland have been to see [EU chief negotiator] Michel Barnier [and] back a sensible backstop.

"The majority of people in Northern Ireland are looking for something quite different from what the DUP is looking for, and yet the DUP is given this platform as if it speaks for Northern Ireland."

Mr Coveney also suggested the entire debate over Prime Minister Theresa May's Chequers proposals for the future EU-UK economic relationship, which are hugely unpopular with Brexiteers, was misplaced.

"Nobody's voting on Chequers between now and when Britain leaves the EU," he said, pointing out the UK parliament will only be voting on the framework of a future trade deal with the EU before March next year.

"We're voting on the two documents - a withdrawal agreement that needs to be able to stand up to legal scrutiny and court challenge; the second document is a political declaration on parameters.

"Nobody thinks we can sign off on all the detail [of a future trade agreement] by the end of the year."